Dental implants and methods for extending service life

ABSTRACT

An implant has a proximal protrusion that is distinctly non-round even in a worn state, e.g. square in cross section, and may include radial slots for use in threading the implant into the jaw bone. No forces need be applied directly to the protrusion&#39;s external surfaces when inserting the slotted implant for subsequent osseointegration.

This is a continuation in part of Ser. No. 08/380,850, filed Jan. 30,1995, now U.S. Pat. No. 5,580,246.

BACKGROUND OF THE INVENTION

This invention relates generally to a dental prosthesis and moreparticularly to a dental prosthesis that is attached to an implant inthe bone of a person's jaw.

It is now common when it is desired or necessary to replace a missingtooth or teeth, that the gum is opened and an implant is imbedded in thebone structure beneath the gum. The implant is held initially byfriction in a socket formed in the bone or the implant may be threadedinto the bone. The gum is then closed over the implant and heals. When aproper material is used for the implant, the bone and implant growtogether by a process known as osseointegration so that after severalmonths the implant becomes a permanent part of the bone structure in themouth. Titanium has been an effective implant material.

Many firms manufacture complete systems of dental implants andprosthetic components for subsequent attachment to the implants. In atypical construction, the implant has an axially threaded hole at itstop, that is, the proximal end, near the gum surface. After the implanthas integrated with the bone, the gum of the implant is opened to exposethe tapped hole. Then an abutment is attached to the tapped hole of theimplant and extends to a level above the gum or substantially to the gumsurface. The protruding free end of the abutment is constructed forattachment of a prosthesis. For preventing rotation of the prosthesis,the protruding end of the abutment requires a non-round shape and ahexagonal protrusion has been widely used. The abutment also includes acentral threaded hole concentric with the threaded hole of the implantand extending inward toward the jaw bone.

A false tooth or crown is provided with a hole therethrough, known inthe art as a chimney, and a non-round recess in its base corresponds inshape to the protruding non-round cross section of the abutment.Thereby, the crown can be connected to the abutment and relativerotation between them is prevented so long as critical contours of theabutment and the recess in the crown are maintained.

To prevent the crown from lifting axially from the abutment, a finalscrew, sometimes known in the dental profession as a "gold screw", ispassed into the chimney opening and engages the tapped hole in theimplant by way of the abutment so as to hold the crown axially to theabutment and to the implant. Thus, the crown cannot rotate about theabutment or implant because it is mated with the special contours on theexposed end of the abutment. The abutment is similarly mated to theproximal or outer end of the implant. The crown cannot pull away fromthe abutment when the gold screw has been tightened into place.

Finally, the chimney above the gold screw is filled with a compositematerial that hardens and is shaped as part of the crown to look like anatural tooth.

There are many variations in construction.

In many instances, the crown is attached directly to a non-roundprotrusion of the implant and is held directly to the implant by a goldscrew without use of an intermediate abutment.

The implant is intended to be a permanent fixture in the jaw bone. Theabutment and crown may be replaced if necessary due to damage or poorfit by gaining access to the screw head by way of the chimney, andbacking off the screw so that the crown and abutment, if used, can beseparated from the implant. Thus, repairs may be made of an abutment andcrown with relative convenience.

Whereas dental implantations go back to the days of the Pharaohs inEgypt, use of titanium metal implants that integrate with the boneitself, is a recent development over the last 25 to 30 years. Data sofar available on the service life of such implants, indicate that mostimplants can be expected to have a long service life withoutcomplications of the implant itself. However, in a significantpercentage of implants, a problem arises because titanium is arelatively soft metal. An unacceptable degree of looseness oftendevelops between the implant and the adjacent abutment or crown wherebythere is relative rotation between the implant and the attachedelements. This rotational latitude occurs when the contours of theprotrusion at the proximal end of the implant become worn as a result oflateral forces applied on the protrusion. Such forces are transmittedfrom the crown as the crown interacts with adjacent teeth, and perhapsbones, during the course of chewing, biting and nervous grinding(bruxism). Tremendous rotational forces are known to act on the crown.Once there is some degree of freedom for rotation of the crown relativeto the implant, the non-rounded contours of the implant protrusion tendmore and more toward roundness, and permit more and more rotation. Intime, the connection between the implant and the abutment and crownconnected thereto does not prevent rotation and is unacceptable.

In these types of failure, for example, where the original protrusion onthe implant was hexagonal in shape, it has been found that the cornersof the hexagonal shape have been rounded to such a degree that it is notpossible to attach a new crown or abutment and prevent rotation relativeto the implant.

As stated, this type of rounding on the implant protrusion occurs duringnormal use of the prosthesis in biting and chewing. Also, the contoursof the implant protrusion may become distorted, especially unfavorablyrounded or stripped, during the process of threading the implant intothe jaw bone. This occurs because the implant protrusion is the means bywhich the driving tool engages the implant. Therefore, when hard bone isencountered, it is possible that an implant may be damaged beyondusefulness by an ill fitting socket type wrench that engages the outersurfaces of the protrusion and is used to drive-in the implant.

This situation, though costly, is not catastrophic when initiallyinserting an implant in that the damaged implant may be removed and anew one may be inserted. Unfortunately, after the implant has beenjoined to the jaw bone by osseointegration, and after years of thiscondition, it is extremely difficult, costly, and the cause ofconsiderable suffering to the patient, to attempt to remove a damagedimplant and replace it with another.

What are needed are a method to rehabilitate in the mouth a damagedimplant that no longer holds the crown effectively against rotation, andan improved implant that better resists rotation of an attached abutmentand/or crown and thus has an extended service life.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the invention to provide a method forrehabilitating the proximal end of an implant so as to prevent relativerotation of abutment or crown elements after the initial attachmentmeans has failed.

Another object of the invention is to provide an improved dental implantthat reduces the hazards of damage to the implant attachment protrusionduring installation and of damage due to crown rotation during normalusage over the life of the prosthesis.

Yet another object of the invention is to reduce the occasions when animplant that has osseointegrated with the jaw bone needs removal in itsentirety.

In a method to rehabilitate or repair an implant having a damagedproximal protrusion, such that there is unacceptable rotation betweenthe implant and an attached abutment and/or crown, a jig is slipped overthe remaining implant protrusion after removal of the crown andabutment. Guided by the jig, a burr forms radial slots, or otherindentations, in the outer surface of the implant adjacent to theprotrusion. The slots or other indentations may extend into the implantprotrusion. A new abutment (and/or crown) is prepared by techniques thatare a modification of casting techniques well known in the dental arts.The bottom surface of the prosthetic device that engages the implantprecisely engages the newly-added radial slots or indentations on theimplant such that when the final screw is tightened into place, rotationbetween the implant and the attachments is prevented.

Modified analog implants, copings, and abutments facilitate the method.

Further, an improved implant in accordance with the invention has aproximal protrusion that is generally square in cross section andfurther includes radial slots for use in threading the implant into thejaw bone. Thereby, no forces need be applied directly to theprotrusion's external surfaces when inserting the implant for subsequentosseointegration. In this way, the surfaces of the protrusion that areused to maintain the abutment and/or crown against rotation relative tothe implant are not subject to inadvertent damage during installation ofthe implant in the jaw bone. Further, the rotation resisting surfaces ofthe squared protrusion are broad and generally continuous and adjacentsurfaces meet at 90° angles, or less. Forces tending to rotate the crownhave little effect on the holding power of the proximal protrusion evenshould the edges of the protrusion be removed or become rounded.

In accordance with the invention, radial slots may be formed into theprotrusion itself or extend radially from the base of the protrusion.Slots may be provided in different radial directions.

Further, the slots may be omitted whereby the implant, if threaded intothe jaw bone, is driven by a tool applied to the protrusion. Many crosssections are available for the protrusion to provide a non-round shape.These cross sections include regular and nonregular convex and nonconvexpolygons, rounded shapes, and fluted surfaces.

The invention accordingly comprises the several steps in the relation ofone or more of such steps with respect to each of the others to effectrehabilitation of an implant, and the apparatus embodying features ofconstruction, combinations of elements and arrangement of parts whichare adapted to effect extended service life for such implants, all asexemplified in the following detailed disclosure, and the scope of theinvention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the invention, reference is had to thefollowing description taken in connection with the accompanyingdrawings, in which:

FIG. 1 is a front elevational view, in section, of an implant of theprior art;

FIG. 2 is an exploded view, in perspective, of the dental implantconstruction of FIG. 1;

FIG. 3 is a top view of the implant of the prior art;

FIGS. 4a, b are top and bottom views, respectively, of a repairedimplant and modified crown, in accordance with the invention;

FIGS. 5a, b are respectively an elevational view, in section, and abottom view of a notching jig in accordance with the invention;

FIGS. 6a, b are front and top views respectively of an abutment inaccordance with the invention;

FIG. 7 is a perspective view of a modified implant analog;

FIG. 8 is a flow diagram of methods in accordance with the invention toproduce a repaired dental prosthesis;

FIG. 9 is a top view of an alternative embodiment of an implant inaccordance with the invention;

FIG 10a and 10b are a top and side elevation, in section, of anotherimplant of the invention;

FIGS. 11-14 are additional embodiments, in top view, of implants of theinvention;

FIG. 15 presents top views of alternative bosses in accordance with theinvention;

FIGS. 16-18 are further alternative embodiments, in top view, ofimplants in accordance with the invention; and

FIGS. 19a-19m are further alternative embodiments, in top view, ofimplants in accordance with the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention is concerned with the problem of rotation of acrown, or an abutment and crown, relative to a dental implant to whichthe abutment and crown are attached. In many applications, the abutmentis omitted and a crown attaches directly to the implant. In everyinstance, the inherent problem of relative rotation is substantiallysimilar. Accordingly, any description that includes an abutment, or anydescription that omits use of an abutment, is also applicable to theother construction.

In FIGS. 1-3, a dental prosthesis 10 of the prior art includes animplant 12 embedded in the spongiosa 14 of the jaw bone. After a healingperiod of several months, the implant 12 has become part of the bonystructure by the known process of osseointegration. The implant 12protrudes through the cortex 16 of the jaw bone, and the gum tissue 18conceals the proximal end of the implant 12. A tapped hole 20 opens atthe proximal end and is accessible between the parted gum tissue 18. Thecrown 22 usually aligns with the tapped hole 20 in the implant 12.

A hexagonal boss 42 on the implant 12 protrudes above a surface 44 of aflange 45 of the implant 12. The base 46 of the crown 22 includes ahexagonal socket 48, whereby the crown 22 can be removably connected tothe implant 12 with the implant boss 42 engaged in the hexagonal socket48 of the crown 22. Thereby, rotation of the crown 22 about thelongitudinal axis 49 of the implant 12 is prevented by the hexagonalcross-section.

Threads 32 of a screw 34 engage the tapped hole 20 until a bevel surface36 on the screw head 38 engages a shoulder 40 on the crown 22.Tightening the screw 34 into the threaded hole 20 of the implant 12draws the crown 22 into a rigid axial connection with the implant 12 andconsequently with the bony structure 14, 16 of the jaw.

In attaching the crown 22, the screw 34 is tightened by means of anAllen-head type tool that engages the hexagonal socket 50 in the screwhead 38. Then the chimney 30 is filled with a filler material, known inthe dental arts, and the exposed surface of the filler material iscontoured to match the remainder of the crown.

The implant 12 may be screwed into the jaw bone or may be pressed into aprepared socket. When a titanium implant 12 is used, as is the currentpractice, it is anticipated that an osseointegration process will bindthe implant 12 permanently into the jaw after a period lasting three tosix months. Then, the crown 22 is prepared to custom fit the integratedimplant within the space available between adjacent teeth. Frequently, agum shaping device or healing cap (not shown) is threaded into thetapped hole 20 and maintained in place while the gum heals after theinitial implantation. When screwed into the bone, the implant 12 isdriven by attachment of an Allen-head type tool onto the protruding boss42. To reduce any hazard of damaging the surfaces of the protrusion 42while tapping (threading) the socket in the bone, an analog implant (notshown) of material stronger than titanium, e.g. stainless steel, may beused. After the socket is tapped, the actual implant 12 is threaded intothe prepared opening. Once the final setting is made, hopefully, theimplant will never need removal.

FIG. 3 is a top view of the implant 12, clearly illustrating a hexagonalboss or protrusion 42 having six planar surfaces 52 that intersect atapexes 54 with 120° angles between them. However, as the apexes 54become rounded, as illustrated at 54', due to forces exerted on thecrown during chewing, biting, etc., the overall cross section of theboss 42, takes on a circular shape and resistance to further rotationalrelative motion between the implant 12 and the crown 22, attachedthereto by engagement with the boss 42, diminishes to the point wherethe utility of the prosthesis is compromised. Repair or replacementbecomes necessary.

Whereas an attached crown, which is damaged, can be replaced withrelative ease, there is no purpose to such a procedure unless steps aretaken to prevent future relative rotation between the crown 22 and theimplant 12.

By a rehabilitation method in accordance with the invention, theproximal end of the implant 12 is modified in vivo by the addition ofslots 56 (FIG. 4a) formed into the surface 44 of the implant 12 adjacentto the boss 42. ("prime" reference numerals, e.g., 12', 22', indicatemodified or repaired elements.) The ends 58 of the slots 56 preferablydo not extend to the circumference 60 of the flange 45 so as to preventbacterial action which might otherwise occur in those regions, if theslots 56 left small open pockets at the crown/implant interface.

The lower or bottom surface FIG. 4b of the crown, which may incorporatean abutment, includes a recessed socket 48 wherein the boss orprotrusion 42, although deformed, extends. To complement changes in theimplant, the undersurface of the new crown 22', in accordance with theinvention, also includes protrusions 62 corresponding with the shapesand positions of the slots 56 newly-formed in the implant 12' such thatwhen the prosthesis is assembled, the radially oriented protrusions 62on the crown 22' engage in the slots 56 on the implant 12' and therebyprevent rotational relative motion between the implant 12' and the crown22'.

Next will be described methods, in accordance with the invention, forrehabilitating an implant 12 in the mouth to provide the constructionsillustrated in FIGS. 4a, b, when the implant can no longer maintain theproper rotational orientation with the crown 22 of the prosthesis. Thisoccurs, for example, because the apexes 54 on the hexagonal boss 42 havebecome rounded due to the inherent softness of the titanium metal andthe tremendous forces exerted on the crown during chewing, biting, etc.

First, the proximal end of the implant 12 is exposed by removal of thecrown 22 and an abutment, if one was used intermediate the implant andthe crown. As a result, the protrusion or boss 42 and the surface 44 onthe implant are exposed to view (FIG. 3).

These external elements are removed after exposing and backing out thescrew 34 via the chimney 30. Then a notching jig 64 (FIGS. 5a, b) isplaced onto the implant 12. The notching jig 64 includes a bottominterface surface 66 that rests on the exposed flange surface 44 of theimplant 12. A hexagonal socket 68 extends into the bottom surface 66 ofthe jig 64, having dimensions such that the protrusion or boss 42 on theimplant 12 enters the socket 68 when the surfaces 66, 44 of the jig andimplant are in contact. It should be understood that the socket 68 maybe round in section so long as the boss 42 enters and allows seating ofthe jig 64 with a relatively snug fit to provide alignment.

The notching jig 64 has a long stem with a longitudinal opening 70through which a threaded screw (not shown) is inserted so as to engagethe central opening 20 in the implant 12. Thus, the jig 64 is axiallyfixed into position on the implant 12 even though the boss 42 is worn.Guide holes 72 extend from a rear shoulder 74 on the jig 64 to theinterface surface 66. Four guide holes 72 are illustrated; in practice,two guide holes are sufficient when two slots 56 are to be formed in theimplant surface 44.

With the notching jig 64 in place on the implant 12, the dentalpractitioner runs a rotating burr through the guide holes 72, in turn,and forms indentations 56 into the upper surface 44 on the flange 45 ofthe implant 12. A stop on the burr or shoulders (not shown) within theguide holes 72 limit the depth of the indentation 56 formed in thesurface 44 of the modified implant 12'. Thus, a configuration as shownin FIG. 4a, albeit with less precisely rectangularly shaped slots 56, isproduced. The burr shaft diameter, used to make the indentations orslots 56 on the surface 44 of the implant, may be less than the diameterof the guide holes 72, giving the practitioner latitude of motion so asto shape the slots 56 in the implant 12'.

Alternatively, the guide holes 72 may be radially oriented ovals (notshown), extending inwardly toward the opening 20 so that the burr mayprovide extended slots in the implant 12 that cut into the protrusion42. These elongated slots, the extensions indicated in FIG. 4a withbroken lines on the boss 42, may extend nearly into the tapped hole 20.The longer slot provides a stronger engagement with a driving tool andwith the modified crown, which is provided with longer protrusions 62.

In another embodiment of the method for repair, a notching jig mayprovide slots only into the boss 42 and not in the flange surface 44.

Repair of an implant already imbedded in the jaw bone andosseointegrated has been described above, describing the indents formedinto the implant as "slots". It should be understood that indentationshaving contours other than the radial slots illustrated in FIG. 4A maybe provided in the exposed surface of the implant so long ascorrespondingly configured protrusions are provided on the matingelement, for example, the crown or abutment.

It is now necessary that the abutment and crown which ultimately attachto the modified implant 12' be made to precisely mate with the slots 56(or other indentations) formed on the surface 44 of the implant. For thesake of the following description of repair procedures, it is assumedthat no separate abutment element is used intermediate the implant andthe crown in the completed prosthesis. Further, generally rectangularslots are described; the procedures also apply to indentations of othershapes.

How to make a crown for attachment to an osseointegrated implant in thejaw is well known in the art of dental implants. The same basicprocedures are followed in making a crown for the now-modified dentalimplant 12', which is still embedded in the jaw bone, however withslight changes in the elements that are used to accommodate the slotsnow formed in the flange surface 44 of the implant 12'. The finishedcrown must have protrusions on its lower inner surface that interfacewith the implant to complete the prosthesis.

Therefore, conventional fabrication techniques using a direct pick upimpression or an indirect impression would readily be implemented bythose skilled in the implantation art without further explanation.However, a brief description (and flow diagram FIG. 8) is given ofseveral techniques to indicate how the modifications made at theproximal end of the implant affect the procedures.

In a direct pickup technique, after notches or slots 56 are prepared onthe implant 12' with the notching jig 64, as described above, a directimpression of the modified top of the implant 12' is made by customizinga resin UCLA-type abutment, using a well-known auto-polymerizing resin.FIGS. 6a, b illustrate a customized resin UCLA-type abutment 76 made ofplastic and having teeth 78 with novel dove-tail spaces 80 between themsuch that impression material after hardening, will not separate fromthe abutment although the impression material does bond to the resinabutment.

The customized abutment 76 is attached to the implant 12' by a guide pin(not shown) that passes through the longitudinal opening 82 in the stem84 of the abutment 76 and engages the tapped opening 20 in the implant12'. Then the impression material is applied to fill the spaces betweenthe abutment 76 and the implant surface 44. After the impressionmaterial has hardened, the guide pin is unscrewed from the implant 12'and the abutment 76 is removed. Covering the end 86 of the abutment 76that opposed the implant 12', protrusions 62 are present exactlycorresponding to the slots 56 newly formed on the implant 12'.

Then, the customized abutment impression (not shown) is cast into astrong, rigid material e.g. metal. The resultant metal abutment isplaced over the implant 12' in the jaw, and is secured in place with aguide pin that engages the central opening 20 of the implant 12' bypassing through a central opening in the metal abutment that correspondsto the opening 82 that was in the customized UCLA-type abutment 76. Theprotrusions 62 are seated in the implant slots 56.

Then a pick-up impression is made in the mouth in the conventionalmanner, that is, a window is cut in the top of an impression tray; thetray is filled with impression material and some of this material ispositioned around the abutment. Then the filled impression tray isplaced over the implant 12' and metal abutment with the guide pinprotruding through the impression material and from the upper surface ofthe tray. After the impression material has hardened in the tray, theguide pin is unscrewed and the impression tray with the metal abutmentnow embedded in the impression, is removed from the mouth. Theprotrusions 62 on the face of the metal abutment are visible in theimpression.

A modified implant analog (stainless steel) having slots that correspondwith the slots 56 which were formed using the jig 64, is positioned onthe abutment with the slots on the implant analog receiving therein theprotrusions 62 on the metal abutment, which was embedded in theimpression. The implant analog is fixed to the abutment with a guidepin, and the assembly is poured in stone, that is, a rigid modelingmaterial. After hardening, the guide pin is removed, and the impressioncontaining the abutment is separated from the stone.

The stone model now positively replicates the portion of the jawincluding the implant 12'. The model includes the analog implant withslots having the exact same dimensions and orientation as those slots 56in the actual implant 12' in the jaw bone of the patient.

The metal abutment is now removed from the earlier impression material.The metal abutment was made with protrusions 62 that exactly mate withthe analog implant. From this state, a crown is fabricated by well knownprocedures. The crown incorporates the metal abutment, thus assuring aperfect fit for the crown in the mouth.

Rotation of the crown relative to the modified implant 12' is preventedby engagement of the protrusions 62 from the abutment with the slots 56in the exposed surface 44 of the implant 12'.

In a conventional indirect impression technique, slots 56 (FIG. 4a) areprepared in the implant 12 in the jaw using the notching jig 64. Animpression coping is attached to the implant 12' using a guide pin (notshown); the impression coping is conventional except that it hasprotrusions on its lower surface that correspond with the slots 56 madein the actual implant 12 when the notching jig 64 was used. The drawingof the bottom of a crown (FIG. 4b) in accordance with the invention alsoillustrates the modifications (protrusions) to a conventional impressioncoping's bottom interface surface. Thus, a proper engagement between theprefabricated coping and the implant 12' is assured.

Then an impression tray with a window cut out of the top is placed overthe implant and surrounding portion of the jaw so that the guide pinprotrudes. The tray is filled with impression material in a conventionalmanner. After the impression material has set, the guide pin isunscrewed and the impression is removed from the mouth. An implantanalog (e.g. stainless steel) is then abutted with the coping in theimpression, with slots being provided on the implant analog to mate withthe protrusions, which are extending from the surface of the impressioncoping. After the implant analog abuts the coping in the impression, theanalog and coping are secured together with a guide pin, and a model ispoured in stone. The stone model replicates, at least partially, the jawof the person, however, with the proximal end of the implant analogexposed to view, including its slots in the proper orientation. Then acrown is fabricated by conventional procedures. New materials, namelynylon, gold and aluminum oxide (Al₂ O₃) may be used in fabricating thecrown on the stone model in this technique.

In the above methods, it has been assumed that the drill jig 64 is usedin modifying the implant 12 in the jaw. When this is done, the hardware,namely the copings and analog implants, are pre-manufactured,off-the-shelf items with protrusions and slots that will fit or matchthe slots that were made in the actual implant in the jaw bone.

However, many practitioners will prefer not to use such a jig 64 andwill instead produce a variety of indentations of their own preferenceon the surface 44 of the implant 12 in the mouth. In such a situation,pre-manufactured implant analogs and pre-manufactured copings with theproper patterns of slots and protrusions, as required, will not beavailable off-the-shelf.

Therefore, to practice the above procedures, it is necessary to firstmake a direct pick up from the implant 12' in the mouth, using acustomized UCLA-type abutment 76 (FIGS. 6a, b) as described above. Thisimpression is then cast in metal and the first procedure as describedabove is followed with the exception that a modified implant analog mustbe used in the stone-pouring step. This modified implant analog (FIG. 7)does not have a flange 45 or boss 42 but is primarily a shank that isinternally threaded. Before casting in stone, the modified implantanalog is held to the metal abutment in the earlier-formed impression bya guide pin that threadably engages the analog. Then the stone ispoured. (Epoxy may be used alternatively in pouring this model) Thestone model of the jaw will have the central threaded opening of theanalog implant exposed to view. However, the surface with thecorresponding slots of the true implant is reproduced in the stonematerial. From that state, fabrication of a crown is conventional, asbefore.

Next, an embodiment of an implant in accordance with the invention isdiscussed, which will reduce the hazards of stripped and damaged bosssurfaces that would in time prevent proper mating with an abutmentand/or crown. The same reference numerals are used in the description ofthe improved implants where elements correspond to those of FIGS. 1-6.

In an implant 90 of FIG. 9, a boss 92 having a cross section that is arectangle, in this instance a square, as compared to the hexagonal bossof the prior art, is elevated above the surface 44 of a flange 45 on theimplant 90. As in the earlier embodiments, a tapped hole 20 is at thecenter of the surface 44, and a screw 34 ultimately seats in the hole 20to hold a crown, with an abutment in place. Short slots 94 are recessedinto the surface 44 at opposed sides 96 of the square boss 92. The slots94 do not reach to the outer circumference 60 of the flange 45 in orderto avoid potential bacterial activity at those sites.

Each of the sides 96 of the boss 92 have a greater continuous length asviewed in FIG. 9 than any single side of the hexagonal boss 42 of theprior art (FIG. 3) for a corresponding circumference 60. Thus, when, forexample, a crown with a square recess on its bottom surface is fitted tothe implant 90 with a snug fit to the boss 92, and is tightened in placewith a screw 34, there is little likelihood that the attached crown willever rotate relative to the implant. The parallel opposed sides 96 andincluded 90° angle of the square boss 92 prevent rotation even if thecorners of the square-shape should for some reason become rounded.

The boss 92 is bevelled (similar to FIG. 10b) at its upper edges 93.Also, the boss 92 may rise vertically from the general plane of thesurface 44 or there may be a slight taper in the direction away from theflange 45. Such a construction makes for easier entry of the boss 92into a recess, which may also have tapered sides, for example, in acrown.

Additionally, the slots 94 are provided for the purpose of screwing theimplant into the bone. The bone is frequently pretapped using a dummy(analog) implant that is made of tougher metal or plastic than thetitanium implant itself. The tool which is used for threading theimplant 90 into the bone of a patient (not shown) is constructed suchthat it rotates the implant 90 by tool engagement with the slots 94 andnot because of any driving engagement with the sides 96 of the boss 92.Thus, the surfaces of the boss 92 do not become damaged by the insertiontool upon the initial installation of the implant into the jaw bone, andthe contours of the boss 92 are preserved for accurate and effectivemating with the abutment and/or crown.

To further assure the fixed relative position between the implant andthat which is externally attached to it, the abutment or crown thatinterfaces with the implant 90 may be made with protrusions that engagein the slots 94 at the interface.

It should also be understood that because of the increased strength ofthe square boss 92, the boss may be used when threading the implant intothe jaw bone, and the slots 94 may be omitted. In such a use of the boss92, the likelihood of serious damage to its surfaces, so as to renderits attachment to an abutment and/or crown rotationally unacceptable, ismuch less than with the hexagonal boss 42 of the prior art.

The implant 98 of FIGS. 10a, b, is similar to the implant 90 of FIG. 9except that the slots 94' extend through the boss 92 near to the centralopening 20, such that a blade type tool may be used in the slots 94'when screwing the implant 98 into the jaw bone.

The slot 94' may penetrate in depth into the upper surface 100 of theboss 92, as illustrated with the solid lines in FIG. 10a. On the otherhand, the slot depth may be extended (not shown) substantially, eveninto the flange 45, that is, below the surface 44 of the flange 45. Inany event, the slot ends 102 do not extend through to the outerperiphery 60 of the flange 45 to reduce hazards of bacterial activity.It is also desirable for similar reasons that the slots do not open intothe tapped hole 20.

For the purpose of increased strength of the boss 92, if needed, it ispossible in manufacture to enlarge the size of the generally squareshape and possible lose the perpendicular intersections as indicated bythe broken lines 104 in FIG. 10a. (In all constructions, there is atrade-off between the implant strength and the strength of the attacheddevice.)

In FIG. 11 another embodiment of an implant 106 in accordance with theinvention is shown having a generally square elevated boss 92 with slots94" running diagonally across the square and extending proximate to thecentral opening 20. This provides a longer slot length in the bossitself, but is otherwise similar to the implant 98. As with the implant98, the slot 94" can penetrate the boss 92 to various depths and mayextend to and penetrate into the flange 45.

Another alternative embodiment (FIG. 12) provides an implant 108 with anelongated rectangular boss 109 with perpendicularly oriented slots 111that extend proximate to the central opening 20. The slots arepreferably used exclusively for threading the implant into the jaw boneand the boss 109 is preferably used exclusively for holding the abutmentand/or crown against rotation. However, with a proper tool (not shown)applied to the boss, the implant may be threaded into the jaw bone.

In FIG. 13, an implant 107 includes a generally triangular boss 113 thatis penetrated by slots 115, 116 of extended length and selectable (inmanufacture) depth that pass through an apex of the triangle.

In FIG. 14, an implant 117 includes a pair of rectangularly shapedbosses 119 on opposite sides of the tapped hole 20. A pair of radialslots 121 extend from opposite sides of the tapped hole 20. In usingsuch an implant 117, the crown 22' may have a recess (not shown) on itsbottom of rectangular shape that receives both bosses 119 in a singlecavity. The bottom surface of the crown may also have protrusions toenter the slots 121. Alternatively, the bottom surface of the crown mayhave two smaller rectangular recesses with each of the bosses 119 beingreceived in a respective recess. Protrusions to engage the slots 121 mayalso be a part of the bottom surface of the crown.

In installing such an implant 117 into the jaw bone, it is preferablethat a tool that engages the slots 121 is used without engagement withthe protrusions 119 for driving purposes. However, it should beunderstood that the bosses 119 can be used in driving the implant 117into the jaw bone and a driving tool can be made for that method.Further, both the slots and the bosses may be used when driving theimplant into the jaw bone when a properly mating tool is provided. Theimplant in FIG. 14 may be considered as a variation on the implant ofFIG. 12 in that the two bosses 119 are at opposite ends of an elongatedrectangular shape.

In each embodiment, it is intended that the implant be threaded into thejaw bone using only the slots in the proximal implant end. Nevertheless,it is recognized that the boss outlines, whether square, elongatedrectangular, triangular, etc., because of their cross sectional bulk andlong sides with reduced intersection angles present considerably moreresistance to deformation than the prior art hexagonal cross section ofthe boss 42 (FIGS. 1-3).

Further, it should be understood that the hexagonal boss, or any shapeof the prior art, may be retained (FIG. 4) in an improved implant withextended slots formed through the boss itself, extending toward thetapped opening 20. In such a modified conventional implant or newmanufacture, the implant may be tapped into the bone at its finalinstallation using the slots, without reliance on the contours of thehexagonal boss itself. In this way, the boss is protected from damageduring installation of the implant.

Whereas the figures have illustrated bosses having different polygonalcross sections that are defined by straight lines and crispintersections of those lines, it should be understood that rounded andbevelled edges, are intended to fall within the scope of the invention.Additionally, any generally axially oriented side surface of a boss mayinclude a bulge or concavity so long as the basic polygonal shape isretained. For examples, FIG. 15 illustrates an elongated rectangularboss that has rounded ends so as to be an oval b. The long sides areconcave in a and bulging in c. These are variations of the boss, forexample the rectangular boss in FIG. 12, and for the purposes of thisdisclosure, are considered to be elongated rectangular (polygonal),possibly including straight and rounded segments, and fall within thescope of the invention. As stated, a trade off must be made between thestrength of the boss and the strength of the crown to be attachedthereto. The concave configuration a may be used where greater strengthis required in the crown, and the bulging configuration c in FIG. 15 maybe used where the boss requires increased strength.

FIGS. 16, 17 and 18 illustrate further alternative embodiments inaccordance with the invention of bosses provided with other polygonalcross-sections. In FIG. 16 four rectangular protrusions or bosses 123project from the surface 44 to be received in corresponding matingrecesses on the crown or abutment. Slots (broken lines) or indentationsin the surface 44 may optionally be positioned between the bosses 123.Two or four slots may be used. The plurality of protrusions or bosses123, considered together, provide a non-round shape.

FIG. 17 illustrates a star-shaped polygonal boss 125 extending above thesurface 44. Slots or indentations in the surface 44 may optionally beprovided as illustrated with the broken lines.

FIG. 18 illustrates a multi-sided polygonal boss 127 rising from thesurface 44 in the form of a trefoil. Again, optional slots areillustrated in broken lines as a trio symmetrically positioned in thesurface 44 for use in driving the implant into the bone upon initialimplantation.

Additionally, in the discussions above, the implants are described ashaving a central tapped opening 20. However, implants are known in theart wherein the central opening is not tapped and may have a non-roundcross-section. In such cases, the crown assembly has a post that extendsinto the central opening of the implant and an adhesive is used toprevent axial motion of the crown relative to the implant after theadhesive has set. A non-round boss as described above in accordance withthe invention prevents the rotation of the crown relative to theimplant.

Further, the use of screws that pass through the jaw bone and theimplant, and in some instances through the post on the crown that isreceived in a central opening of an implant, is known in the art, forexample, U.S. Pat. No. 5,542,847. All such means for maintaining theaxial relationship between the crown and the implant when combined withthe bosses, slots etc. in accordance with the invention, are intended tofall within the scope of the invention.

Generically speaking, the cross-sectional shape of the boss inaccordance with the invention is made non-round such that should thelinear edges extending from the surface 44 become rounded there wouldremain a distinct non-round cross section for the boss. The hexagonalshape of the prior art and any regular polygon cross section havingfive, six or more regular sides is vulnerable to circular rounding asvertical edges become worn.

On the other hand, convex polygons as shown, for example, in FIGS. 9-16,present non-round cross sections for the bosses even when the verticaledges become worn and rounded. Additionally, many nonconvex polygonswould make excellent boss cross sections and retain their non-roundshape and utility even when the linear axial edges are rounded. Further,in production such bosses can be made with beveled or rounded edges, andstill be effective for implants.

Further, a generally circular boss cross section can be given holdingpower against turning by an abutment or crown by use of axially orientedflutes that are formed internally, or externally as teeth. Basic shapes,such as a triangular or square cross section boss may also havesupplemental internal or external flutes. Regular hexagonally shapedbosses, by addition of internal and/or external flutes or otherformations, maintain a non-round cross section when the axial edges arerounded.

FIGS. 19a-19m show further alternative embodiments of implants inaccordance with the invention. In each instance the protrusion from thesurface 44 provides a distinctly non-round cross section while providinggood anti-rotational anchorage for an abutment or crown combinationregardless of wear that may occur along the vertical edges, as seen inthe top views in FIGS. 19a-m. Each implant has a central opening 200that may be threaded or non-threaded depending upon the construction ofthe prosthesis.

Bosses with cross sections that are convex polygons are illustrated inFIGS. 19d, f, g, and i. FIG. 19c can be considered as a combination oftwo convex polygons (triangles) in opposed positions relative to theopening 200, or the cross section of FIG. 19c can be considered in itsentirety as a nonconvex polygon.

Nonconvex polygons are illustrated in FIGS. 19a, b, e, j, and m. FIGS.19h and 19k illustrate generally circular bosses that have been givenanti-rotational holding power for an abutment or crown by means ofinternal flutes 201 and external flutes 202, respectively. FIGS. 19g and19i show cross sections that are distortions of regular hexagons suchthat a non-round shape is provided even if the vertical edges at thevertices of intersecting sides were rounded.

Each of the polygons can be altered such that sides become concave orconvex curves and corners can be rounded so long as the resultant shaperetains the desired non-round characteristic that resist turning andwear by an attached prosthesis element. For example, the boss of FIG.19g takes on a teardrop shape when the vertical edges are rounded. Forenhanced holding power, internal or external flutes may be added to anyside surface of the cross sections.

FIG. 191 illustrates the use of circular bosses or protrusions 204 in asymmetrical distribution around the central opening 200. Three, four, ormore such protrusions 204 may also be used. The illustrated combinationof protrusions in FIG. 191 can be considered a variant of the crosssection shown in 15b. A driving tool usable on the configuration of 15bmight also serve with the embodiment of FIG. 191. The combination ofprotrusions 204, considered together, provides the desired non-roundcross section.

In each of the embodiments 19a-m, indentations (not shown) may beprovided into the surface 44 for use in threading an implant into thejaw bone, as discussed above.

For the purposes of the descriptions above and the claims that follow,the definitions of different polygons and their features are based uponthe school text: Addison-Wesley Geometry, by Stanley R. Clemens, PharesG. O'Daffer, Thomas J. Cooney, John A. Dossey; Addison-Wesley PublishingCo., Inc. Menlo Park, Calif. (1994). In particular, pages 135-140 andlater pages, are a source of definitions.

A convex polygon is defined as one in which all diagonals are interior.A nonconvex polygon is one where not all diagonals are interior. Aregular polygon is equiangular and equilateral. A trapezoid is aquadrilateral polygon with one pair of parallel sides. A polygon has nsides with the sides meeting at vertices.

Thus, methods for repairing damaged implants in the mouth, and improvedimplants have been presented. All of those devices that engage therepaired implant, are provided with recesses and protrusions, asrequired. However, a crown, for example, having a recess with a squarecross section so as to match an implant of FIG. 10a, need not haveprotrusions that match the slots 94', as these slots are basicallyintended for installing the implant in the jaw bone. Nevertheless, as aredundancy measure and for additional anti-rotation resistance,protrusions on the crown's lower surface that correspond with the slotsmay also be included in conjunction with the squared recess.

It is contemplated that in practicing the methods, a kit of parts willbe purchased from a dental supplier. The kit for those practitionersusing preferred methods includes a notching jig 64 and an appropriateburr (not shown) to fit the guide holes 72. Also in the kit may be animplant analog having preformed slots 56 on its proximal end, and animpression coping having protrusions 62 on its lower end. A modifiedUCLA-type abutment with dove-tail teeth may also be in such a kit,although it could be purchased separately. A different kit for apractitioner who prefers not to use the notching jig may instead includea UCLA-type abutment and a modified implant analog that has no flange45.

It should also be understood that a reversal of features is intended tofall within the inventions scope. Thus any boss cross-section which hasbeen described as protruding from the flange surface 44 may also beformed (and viewed in the Figures) as a recess in the surface 44. Insuch a construction the mating crown or abutment is fabricated with acorrespondingly shaped protrusion (or protrusions) that seat(s) in therecess (or recesses).

It will thus be seen that the objects set forth above, among those madeapparent from the preceding description, made in carrying out the abovemethods and in the articles set forth without departing from the spiritand scope of the invention, it is intended that all matter contained inthe above description and shown in the accompanying drawings shall beinterpreted as illustrative and not in a limiting sense.

What is claimed is:
 1. A dental implant for insertion in the jaw bone ofa patient, comprising:an elongated body having a longitudinal axis and aproximal surface generally transverse to said longitudinal axis, a bossextending from said proximal surface, said boss having a transverseface, generally axial extended side surfaces, and a non-round crosssection as viewed along said axis, at least one indentation penetratingat least one of said proximal surface and said transverse face of saidimplant.
 2. A dental implant as in claim 1, wherein said non-round crosssection is polygonal.
 3. An implant as in claim 1 wherein said non-roundcross section is defined by said side surfaces and selected from thegroup consisting of a convex polygon, nonconvex polygon, a closedperiphery of curved surfaces, and a closed periphery being a combinationof curved segments and linear segments.
 4. A dental implant as in claim1, wherein said non-round cross section is selected from the groupconsisting of generally square, hexagonal, pentagonal, elongatedrectangular, oval, triangular, star-shaped, trefoil shaped,trapezoid-shaped, rounded with fluting, polygonal with fluting,nonconvex polygonal, and nonregular polygonal.
 5. An implant as in claim1, wherein said side surfaces have flutes, said flutes being selectedfrom the group consisting of internal flutes and external flutes.
 6. Adental implant as in claim 1, wherein said boss includes a plurality ofprotrusions from said proximal surface, said protrusions from saidproximal surface considered together providing said non-round crosssection.
 7. A dental implant for insertion in the jaw bone of a patient,comprising:an elongated body having a longitudinal axis and a proximalsurface generally transverse to said longitudinal axis, a boss extendingfrom said proximal surface, said boss having a transverse face, axialextended side surfaces, and a non-round cross section as viewed alongsaid axis, said non-round cross section being defined by said sidesurfaces and selected from the group consisting of a convex polygon,nonconvex polygon, a closed periphery of curved surfaces, and a closeperiphery that is a combination of curved segments and linear segments,wherein said boss includes a plurality of protrusions from said proximalsurface, said protrusions from said proximal surface considered togetherproviding said non-round cross section.
 8. A dental implant as in claim7 wherein said non-round cross section is selected from the groupconsisting of generally square, hexagonal, pentagonal, elongatedrectangular, oval, triangular, star-shaped, trefoil shaped,trapezoid-shaped, rounded with fluting, polygonal with fluting,nonconvex polygonal, and nonregular polygonal.
 9. A dental implant forinsertion in the jaw bone of a patient, comprising:an elongated bodyhaving a longitudinal axis and a proximal surface generally transverseto said longitudinal axis, a boss extending from said proximal surface,said boss having a transverse face, axially extending side surfaces, anda non-round cross section as viewed along said axis, said non-roundcross section being defined by said side surfaces and selected from thegroup consisting of generally trefoil, quatrefoil, trapezoid, convexpolygon with noncongruent sides, nonconvex irregular polygon, nonregularpolygon, tear-shaped convex, and nonrectangular parallelogram crosssections.
 10. An implant as in claim 9, wherein said side surfaces haveflutes, said flutes being selected from the group consisting of internalflutes and external flutes.
 11. An implant as in claim 9, wherein saidboss cross-section is asymmetric relative to said longitudinal axis.